NEW YORK — When you meet someone for the first time, how do you decide whether or not to trust them? A new study finds you may actually be subconsciously distrustful of people who look like those who have deceived you in the past. Conversely, researchers say, strangers resembling folks you view as reliable are trusted more often.

“We make decisions about a stranger’s reputation without any direct or explicit information about them based on their similarity to others we’ve encountered, even when we’re unaware of this resemblance,” says Elizabeth Phelps, a professor in New York University’s Department of Psychology and the paper’s senior author, in a university release. “This shows our brains deploy a learning mechanism in which moral information encoded from past experiences guides future choices.”

A new study finds that whether or not we trust strangers after meeting them for the first time often depends on how much they resemble other people who we trust or distrust.

The researchers liken the behavior to that exhibited in the famous “classical conditioning” experiment conducted by Russian physiologist Ivan Pavlov and his dog.

While scientists mostly understand how decision-making occurs in the brain in repeated one-on-one interactions, less is known about making decisions when working with strangers.

To test their theory, the researchers set up a trust game for study participants. Individuals had to decide which of three individuals, represented by pictures of their faces, they would entrust a hypothetical investment with. One individual had a high rate of getting good returns and sharing the profits with the participants (highly trustworthy), one had a moderate rate (somewhat trustworthy), and one had a low rate — keeping the profits for themselves (not at all trustworthy).

The second part of the experiment had participants choose partners — again represented by facial images — for another trust game. This new set of partners, unbeknownst to the participants, was actually created using digitally morphed images combining elements from the partners featured in the first experiment. The photos were altered enough that the study participants weren’t consciously aware that these new strangers were similar to the earlier ones.

The researchers found that the more the player resembled the trustworthy individual from the first part of the experiment, the more the participants trusted them. Similarly, participants more often ignored those that resembled the untrustworthy partners,

The researchers say that their findings show that the brain is highly adaptable and that we make moral assessments of strangers based on previous experiences.

“Our study reveals that strangers are distrusted even when they only minimally resemble someone previously associated with immoral behavior,” says lead author, Oriel FeldmanHall. “Like Pavlov’s dog, who, despite being conditioned on a single bell, continues to salivate to bells that have similar tones, we use information about a person’s moral character, in this case whether they can be trusted, as a basic Pavlovian learning mechanism in order to make judgments about strangers.”

The study’s findings were published last week in the journal Proceedings of the National Academy of Sciences.